The purpose of these studies is to relate mosquito exposure to human clinical outcome, especially in children and pregnant women, and to define the basis of the semi-immune state. Previous studies report that malaria infection in a newborn and infants is rare in sub-Saharan Africa. However, our preliminary studies suggest that malaria in newborns may not be as uncommon as previously thought. Aim 1 provides a transition between Project 1 and this project by quantitating sporozoite exposure among young and older subjects. Aim 2 examines the possibility that maternal infection during pregnancy may not only lead to infection of the newborn, but also may condition the newborn and paradoxically decrease the risk of severe disease. In this study we will follow pregnant women until delivery to examine the effects of immunological change associated with malaria. The newborn will be followed from birth to 24 months to determine potential effects of maternal infection during pregnancy on the rate of acquisition of infection or disease during early childhood. Aim 3, which examines the development of the semi-immune state, includes a series of immunologic studies utilizes established antigens as well as GPI. Using a combination of real time PCR to quantitate parasite density and microarray technology to examine gene expression, this proposal has the potential to bring new basic information to bear of the semi-immune state.